Tunneling in single-layer Bi2Sr2CuO6+δ single crystals in high magnetic field

In tunneling experiments with high-quality single crystals of a single-layer cuprate superconductor Bi2Sr2CuO6+δ using the break junction and point-contact techniques at T<Tc, the coexistence of the superconducting-state gap and the normal-state gap was observed. The values of the superconducting energy gap 2Δp−p are in the range from 13.4 to 15 meV (Δp−p=6.7–7.5 meV). The values of 2Δp−p are similar for two samples with Tc=4 K and for two samples with Tc=9–10 K and are independent of the carrier concentration. The normal-state gap, with the magnitude approximately equal to 50 meV, persists at T<Tc and in the magnetic field H≫Hc2 up to 28 T. After the transition of the sample to the normal state, the intensity of the tunneling conductance rapidly decreases with increasing magnetic field strength and temperature. The observed large broadening of the tunneling spectra and large zero-bias conductances can be caused by a strong angular dependence of the superconducting gap. The tunneling results are in full agreement with the data of the angle-resolved photoemission spectroscopy measurements.